JPH10125639A - Polishing method for semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a new oxidation/etching reagent that reduces metal contamination, prevents contamination and coating on a chemical mechanical polishing(CMP) device, does not contain mobile ions, can be safely and easily circulated, and is more stabilized colloidal suspension. SOLUTION: The CMP method uses slurry 22. The slurry 22 contains one or more types of ammonium salt (e.g. ammonium nitrate (NH4 NO3 ) as oxidation/ etching species present in the slurry 22. The slurry is used to polish a metal layer 14. Thereby the ammonium salt does not pose slurry dispersion problems, does not contain metal species or mobile ions, such as potassium, and is environmentally safe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to semiconductor manufacturing methods, and more particularly to chemical mechanical polishing of metals.
oxidation / etching species (et in cal polishing (CMP))
cher species).

[0002]

BACKGROUND OF THE INVENTION Chemical mechanical polishing (CMP) is a well known technique in the semiconductor manufacturing art. The process of manufacturing a semiconductor device includes:
It may often involve a chemical mechanical polishing (CMP) step to improve layer planarity and / or determine conductive interconnects. A commonly used CMP process utilizes abrasive particles suspended in a colloidal slurry. The polishing rate and slurry selectivity can be improved by combining different additives or agents with the slurry. Examples include various ionic salts such as iron nitrate (Fe (NO ₃ ) ₃ ) or hydrogen peroxide.
But oxidizing etc. for metal CMP process
hing reagent). Other reagents also
By combining with the slurry, the mobility or flowability of the slurry is improved, and further mixing of the slurry with the slurry prevents erosion of the polished surface. Many additives or reagents are conventionally known in the art.

[0003] Several oxidation / etching reagents are known. In the first type, the oxidizing / etching reagent used in the CMP slurry contains a metal. Potassium ferric cyanide (potassium) is an example of such an agent.
ferric cyanide, ferric nitrate or cerium nitrate would be conceivable. Metal-based reagents have the problem that metal ions are generated as a result of the oxidation step. These metal ions can contaminate the exposed surface of the semiconductor wafer, which will affect the reliability and functionality of the semiconductor devices on the wafer. In addition, these metallic species (ma
Tallic species) coat / contaminate CMP equipment, creating particle problems and reducing the life cycle of CMP equipment. And this is
This increases the replacement of the polishing apparatus and increases costs associated with the manufacturing process.

[0004] In a second type, the oxidizing / etching reagent used in the CMP slurry contains potassium (K). Examples of such oxidation / etching are potassium iodide or potassium felicide. A reagent using potassium as a base has a problem that potassium ions remain in the slurry as a reaction product of the CMP step. Potassium is a highly mobile ion in the conductive layer of the semiconductor device. Increasing the incorporation of potassium into the substrate layer increases the leakage current in the final manufactured device. Thus, potassium ions can impair the reliability of integrated circuits (ICs).

[0005] A third type is a reagent in which the reagents used as part of the slurry are inherently unstable and cause a slurry delivery problem. Examples of such reagents include hydrogen peroxide (H
₂ O ₂ ). Hydrogen peroxide can decompose to H ₂ O and O ₂ . Such a reaction is carried out in a slurry circulation system (slurry d
slurry pump inside the elivery system
With s), it can be further accelerated. Opened O ₂ results in excessive pressure in the slurry circulating system can become damaged and / or hazardous handling conditions as a result.

The fourth type is that the reagent used in the slurry is strongly alkaline or strongly acidic. An example of a strongly acidic reagent is nitric acid. Extremely high or extremely low pH values (ie, less than 1 or greater than 11) will compromise the colloidal stability of the slurry. Therefore, a strong alkali or strong acid reagent is inconvenient because a slight change in the reagent concentration results in a large change in pH.

[0007] Many of the oxidizing / etching reagents described above
Harm the environment (for example, potassium ferric cyanide (po
tassium ferric cyanide, cerium nitrate
rate) and ferric nitrate) or are expensive (eg, cerium nitrate).
e)).

[0008] Thus, reducing metal contamination, preventing contamination / coating of CMP equipment, free of mobile ions,
There is a need for new oxidizing / etching reagents that are safe and easy to circulate and that are more stable colloidal suspensions. In addition, the price is lower,
A new oxidizing / etching reagent that can be easily disposed of in an environmentally safe manner is desired.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, the present invention uses ammonium salts as oxidizing / etching species in the slurry of a chemical mechanical polishing (CMP) system for polishing metals. Many ammonium salt species (ammoni
Since um salt species) does not contain metallic species, ammonium salts do not significantly contaminate / coat CMP equipment. Furthermore, since there is no metallic species, the upper surface of the silicon wafer is not contaminated by slurry containing ammonium salts. Moreover, the ammonium salt species does not include the potassium or similar mobile ions described above and can easily diffuse across the dielectric material. Therefore, the reliability of integrated circuits (ICs)
It can be improved by using the previously described slurry. In addition, the above-mentioned ammonium salts are not difficult to disperse, and the dispersion problem caused by aqueous hydrogen peroxide (distribution
problems). Ammonium salt slurries are relatively inexpensive compared to other slurries used in the industry. Also, ammonium salts are environmentally safe and can be easily disposed of after use. In short, ammonium based salts as oxidizing / etching reagents in CMP slurries provide a significant improvement over the prior art.

The present invention will be better understood with reference to FIGS. FIG. 1 illustrates a semiconductor device 10. The semiconductor device 10 includes a substrate 12. Substrate 12 is typically a semiconductor substrate, such as silicon, germanium, gallium arsenide, silicon on insulator (SOI) substrate, III-V
And II-IV compound semiconductor substrates, dielectric substrates (PZT, Si
O ₂ ). In addition, substrate 12 is comprised of a dielectric layer and a conductive layer overlying the substrate, and is required for the formation of active and passive devices of one or more integrated circuits (ICs).

Various topographically defined shapes can be patterned and etched on top of the dielectric layer forming the topportion of substrate 12 in FIG. Geometries that can be etched into these overlying dielectric layers of substrate 12 include contact vias, interconnect trenches, dual inlaid structures (a dual damascene process). dual damascene process)) and a similar inlaid structure. After forming these features, a conductive layer 14 is formed over the substrate 12. Conductive layer 14
Is a conductive nitride material, refractory metal
s), refractory silicide, copper,
It can be formed from silver, gold, aluminum, platinum and the like. Due to the underlying inlaid structure or contact, when the conductive layer 14 is deposited, the upper surface of the conductive layer 14 will not be planar. Planarization to shape the top surface of conductive layer 14 to be substantially planar is necessary to form inlaid contacts and / or interconnects.
To determine the interconnects and contacts or plugs from the conductive layer 14, chemical mechanical polishing (CMP) techniques
It is shown using FIGS. FIG. 2 shows a slurry 22, which is applied to cover the upper surface of the conductive layer 14. The slurry may include one or more species that can polish the conductive layer 14.
s). Generally, the slurry 22 comprises one or more types of abrasive species, oxidizing / etching species, oxidizer species, etching species and additives (eg, corrosion inhibitors).
inhibitors), selectivity enhancer
ers) and enhancement additives for slurry circulation (slurry tr)
anseport enhancing additives)).

As shown in FIG. 2, moving the polishing surface 20 (preferably a rotatable polishing pad).
Are positioned to contact the slurry 22. The polishing pad 20 provides mechanical polishing support during the polishing process illustrated in FIGS. 2-6 and provides sufficient slurry circulation in the system 30. Polishing pad 20 is typically formed from a polymer, typically polyurethane. It does not matter whether the polishing surface is moving or the wafer is moving, as long as either the wafer or the polishing surface is moving relative to the other.

In a preferred embodiment, the slurry 22 shown in FIG. 2 comprises an ammonium salt as the oxidizing / etching species. The most preferred embodiment, the slurry 22 is comprised of ammonium nitrate (NH ₄ NO ₃₎ as the oxidizing / etching species. Ammonium nitrate, an oxidizing / etching species in the slurry 22, creates a high polishing rate for aluminum and copper. Also, the ammonium nitrate does not contain metals that contaminate the surface of the integrated circuit or contaminate the device, and the integrated circuit device (integrated circuit device)
facility, easily dispersed and located, strong hydrophilicity (s
oluble in water). Also, the ammonium nitrate provides a high concentration of both cations and anions over a wide pH range and does not provide species that diffuse very well into the dielectric layers of the integrated circuit. In addition, the ammonium nitrate is inexpensive and environmentally safe.

Although ammonium nitrate is preferred, any mono-basic ammonium salt may be used in slurry 22 instead of ammonium nitrate, as described above. For example, ammonium phosphate (NH ₄ PO ₃ ), ammonium sulfate (NH ₄ SO ₄ ), ammonium iodate (NH ₄ I
O ₄ ) can be used for the slurry 22.

As a next preferred embodiment, the slurry 2 shown in FIG.
Instead of ammonium nitrate, di-basic ammonium salts can be utilized. These binary ammonium salts include citrate ammonium ((NH ₄ ) ₂ CH ₆ H ₅ O ₇ ),
Ammonium oxalate ((NH ₄ ) ₂ C ₂ O ₄ ), ammonium sulfate ((NH ₄ ) SO ₄ ), ammonium carbonate ((NH ₄ ) CO ₃ ), ammonium iodide ((NH ₄ ) I) and ammonium tartrate ((NH ₄ ) C ₄ h ₄ O ₆ ) and the like.

As at least one other preferred embodiment,
The ammonium salt containing the metal species is also
22 may be used as an etching / oxidizing species.
Monobasic salts containing these metals are known as aluminum sulfate aluminum salts.
Nmonium (NH_FourA l (SO_Four)_Two), Cerium ammonium nitrate
(NH_FourCe (NO_Three)₆), Cerium ammonium sulfate (NH_FourCe
(SO_Four)_Four), Ammonium iron oxalate (NH_FourFe (C_TwoO_Four)_Three),
Ammonium iron sulfate (NH_FourFe (SO_Four)_Two) Etc. (limited to these)
Not included).

From this point of view, FIGS. 2 to 6 will be described assuming that the etching / oxidizing species of the slurry 22 is ammonium nitrate. In addition, following FIGS. 2-6, the description is made assuming that conductive layer 14 is either copper or aluminum. Restrictions on the materials contained in the slurry 22 and the conductive layer 14 are as follows:
This is briefly illustrated in the description of the next example. Once the conductive layer 14 is brought into contact with the slurry 22, a chemical action takes place. Ammonium nitrate contained in the slurry 22 is first decomposed into anodic ammonium ions (NH ₄ ) ⁺ and cathodic nitrate ions (NO ₃ ) ⁻ .

As shown in FIG. 2, nitrate ions and dissolved oxygen contained in the slurry 22 are dissolved.
gen) thinly oxidizes the upper portion of the conductive layer 14 to form a passivation layer 16. The pH of the slurry 22 affects the stability of the passivation layer 16. Assuming that the pH of the slurry 22 is such that the thermodynamic stability of the passivation layer 16 is reduced, an additive or inhibitor is added to the slurry 22 and the recessed area of the conductive layer 14 (recessed).
areas). In addition, as already mentioned, slurries containing ammonium nitrate have a wide range of
Can be used in the pH range. The pH of a slurry containing ammonium nitrate can be easily adjusted by adding either nitric acid or ammonium hydroxide.
Thus, by controlling the slurry 22, the passivation layer 16 prevents chemical or mechanical shock in the recessed portions of the conductive layer 14, while the top of the conductive layer 14 is removed and planarized. In addition, nitrate ions complex and remove species from conductive layer 14 during polishing (complex remo).
ved). The ammonium ion contained in the slurry 22 is
Used as a counter ion to balance the pH of the slurry 22. The counterion may enrich the ionic species, and in some situations, ammonium ions may complex and remove species from the slurry 22.

FIG. 3 illustrates the effect of the abrasive in the slurry 22 due to the relative movement of the pad 20 and the substrate 12, along the top of the conductive layer 14.
Part 6 has been removed. In addition to the chemical action, a small part of the passivation layer 16 can also be removed by a chemical reaction. Typically, such removal is achieved by abrasive particles, such as metal oxides, in the slurry 22. Alternatively, the polishing pad 20
Is composed of abrasive particles, which are shown in FIG.
As shown, the passivation layer 16 is removed. Note that the recessed portion of conductive layer 14 in FIG. 3 is protected from removal by the recessed portion of passivation layer 16. Therefore, FIG. 3 illustrates that the conductive layer 14 is reduced from the thickness X to the thickness X ′ and is planarized.

In FIG. 4, the passivation layer 1 is formed by the presence of the oxidation / etching species of the slurry 22 as described above.
6 '(shown in FIG. 4) is reformed. The oxidizing and abrasive species in the slurry 22 cause the repeated formation and removal of the passivation layers 16 and 16 '
As a result, the flatness of the upper surface of the conductive layer 14 is improved.

As shown in FIG. 5, this process of protecting the recessed portions of conductive layer 14 while forming and removing the passivation layer continuously reduces the overall thickness of conductive layer 14 in a continuous manner. Go. After a predetermined time, the same surface of the conductive layer 14 is achieved as shown in FIG.

Although the present invention has been illustrated and described in a specific embodiment, further modifications and improvements will occur to those skilled in the art. As already mentioned, all mono- and di-salts, including anodic ammonium ions, can be used as oxidation / etching reagents. Therefore, the present invention is not limited to the specific forms shown.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method for polishing a conductive layer using an ammonium salt slurry according to the present invention.

FIG. 2 is a cross-sectional view illustrating a method for polishing a conductive layer using an ammonium salt slurry according to the present invention.

FIG. 3 is a cross-sectional view illustrating a method for polishing a conductive layer using an ammonium salt slurry according to the present invention.

FIG. 4 is a cross-sectional view illustrating a method for polishing a conductive layer using an ammonium salt slurry according to the present invention.

FIG. 5 is a cross-sectional view illustrating a method for polishing a conductive layer using an ammonium salt slurry according to the present invention.

FIG. 6 is a cross-sectional view illustrating a method for polishing a conductive layer using an ammonium salt slurry according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Semiconductor wafer 12 Silicon wafer 14 Conductive layer 16 Passivation layer 16 'Passivation layer 20 Polished surface 22 Slurry 30 System

Claims (5)

[Claims] 1. A method of polishing a semiconductor wafer (10), comprising: providing a polished surface (20); exposing the polished surface to a slurry (22) containing a monoammonium salt; Moving; contacting a semiconductor wafer having a conductive layer (14) with a slurry (22) while moving the polishing surface; and a conductive layer having an upper surface and positioned on an exposed surface of the semiconductor wafer. Polishing (14), wherein the monoammonium salt in the slurry promotes removal of the upper portion of the conductive layer; (FIGS. 5 and 6). how to. 2. The monoammonium salt is NH ₄ NO ₃ , NH ₄ IO
_4. The method according to claim 1, wherein ₄ , NH ₄ IO ₃ , NH ₄ SO ₄ , NH ₄ PO ₃ . 3. The monoammonium salt is NH ₄ Al (SO ₄ )
₂ , NH ₄ Ce (NO ₃ ) ₆ , NH ₄ Ce (SO ₄ ) ₄ , NH ₄ Fe (C ₂ O ₄ ) ₃ and NH ₄ Fe
The method of claim 1, wherein a is selected from (SO ₄₎ group consisting of _2. 4. A method for polishing a semiconductor wafer, comprising:
Providing a polishing surface (20); exposing the polishing surface to a slurry (22) containing an ammonium salt; moving the polishing surface; having a conductive layer (14) while moving the polishing surface. Slurry semiconductor wafer (2
Contacting 2); and polishing the conductive layer (14) having an upper surface and located on the exposed surface of the semiconductor wafer, wherein the ammonium salt in the slurry is formed on top of the conductive layer. Wherein the conductive layer comprises atoms selected from the group consisting of aluminum and copper. 5. A method for polishing a silicon wafer having an upper metal layer, comprising: a polishing pad having a polishing surface.
A step of exposing the abrasive surface to the slurry (22), the slurry is composed of steps from NH ₄ NO ₃ as an oxidant / etchant; 0) Prepare step the step of rotating the polishing pad; Contacting the silicon wafer (12) with the slurry while the polishing surface is rotating therebetween; rotating the silicon wafer (12) when contacting the slurry (22); contacting the silicon wafer with the slurry; during and are, by the interaction between the upper metal layer (14) and the NH ₄ NO _3, steps of forming a passivation layer over a portion of the upper metal layer (16); said upper and by the slurry Removing the passivation layer from the metal layer, wherein the upper metal layer has a polished and very flat upper surface (FIG. 6). Law.